Air-supported flexible fabric radomes for radar or communications antennas serve as protection from wind, thermal distortions, sunlight, rain, snow, ice, hail, sand, dust and other elements.
For approximately twenty years, the common material used for flexible membrane radomes has been a polytetrafluoroethylene (PTFE) fiberglass composite fabric. While somewhat successful, existing radomes are susceptible to very significant loss of mechanical strength due to creasing and flexing during the manufacturing process and transportation, aging damage due to environmental conditions, as well as stress ruptures or fabric tears when exposed to high loads. These limitations are due in significant part to the material properties of the fiberglass reinforcement used in the fabric construction. Fiberglass as the fiber reinforcement is subject to loss of mechanical strength from fiber-to-fiber abrasion, creasing, folding, and creep rupture. For high survivability applications, a safety margin is required to account for these potential effects. Heavily constructed composite fabrics with large glass fiber bundles become necessary. A heavier construction, however, increases radio frequency (RF) transmission losses decreases receiving sensitivity, and thus requires an increase in the transmission power or the size of radar and communication antennae, at a great cost. Furthermore, practical limitations in the fabric weaving process limit fabric thickness and thus, structural capability. The net result, when all fabric properties are considered, is that product survivability under extreme environmental conditions is not assured. Consequently, compromises between RF performance, structural integrity, and survivability are required.
Using known materials and methods, studies have been performed to investigate increasing the fiber weave density and significant progress has been made. However, poor damage tolerance as experienced in crease fold, flex fold, hydrostatic drum burst tests, and creep rupture failure tensile tests, has demonstrated the need for higher strength damage tolerant reinforcements with suitable radio frequency (RF) transmission characteristics. Significant structural analysis using wind tunnel measurement data and non-linear finite element modeling supports the need for higher strength and strength retention in the radome material. In summary, prior art flexible membrane radomes with high strengths would result in unacceptable radio frequency (RF) losses while the radomes with acceptable RF losses are not generally strong enough in many environments.